<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <title>simple Javascript WebP decoding demo, using Web-Assembly (WASM)</title>
  <script type="text/javascript">
    var Module = {
      noInitialRun : true
    };
  </script>
  <script src="./webp_wasm.js"></script>
  <script type="text/javascript">

'use strict';

// main wrapper for the function decoding a WebP into a canvas object
var WebpToCanvas;

Module.onRuntimeInitialized = async () => {
  // wrapper for the function decoding a WebP into a canvas object
  WebpToCanvas = Module.cwrap('WebPToSDL', 'number', ['array', 'number']);
};

function decode(webp_data, canvas_id) {
  var result;
  // get the canvas to decode into
  var canvas = document.getElementById(canvas_id);
  if (canvas == null) return;
  // clear previous picture (if any)
  Module.canvas = canvas;
  canvas.getContext('2d').clearRect(0, 0, canvas.width, canvas.height);
  // Map this canvas to the default selector used by emscripten/SDL2.
  specialHTMLTargets["#canvas"] = Module.canvas;
  // decode and measure timing
  var start = new Date();
  var ret = WebpToCanvas(webp_data, webp_data.length);
  var end = new Date();
  var decodeTime = end - start;
  result = 'decoding time: ' + decodeTime +' ms.';
  // display timing result
  var speed_result = document.getElementById('timing');
  if (speed_result != null) {
    speed_result.innerHTML = '<p>'+ result + '</p>';
  }
}

function loadfile(filename, canvas_id) {
  var xhr = new XMLHttpRequest();
  xhr.open('GET', filename);
  xhr.responseType = 'arraybuffer';
  xhr.onreadystatechange = function() {
    if (xhr.readyState == 4 && xhr.status == 200) {
      var webp_data = new Uint8Array(xhr.response);
      decode(webp_data, canvas_id);
    }
  };
  xhr.send();
}
  </script>
</head>

<body>
  <p>
    <strong>WebP demo using Web-Assembly</strong> -
  </p>
  <p>
    WASM version of the WebP decoder, using libwebp compiled with
    <a href="https://github.com/kripken/emscripten/wiki">Emscripten</a>.
  </p>
  <p id="image_buttons">
    <input type="button" value="test image!"
           onclick="loadfile('./test_webp_wasm.webp', 'output_canvas')">
  </p>
  <p id="timing">Timing: N/A</p>
  <canvas id="output_canvas">Your browser does not support canvas</canvas>
</body>
</html>
